28 GENERAL OBSKKVATiONS ON 



an instance, are attached to the cainion bone by an elastic sub- 

 stance, found to be a fibrous or ligamentous cartilage; and, through 

 its India-rubber sort of elasticit}^, these bones yield to the impres- 

 sion of weight, and, in a manner more conceivable than demonstra- 

 ble, descend, and spring up again into their places the instant the 

 pressure is taken off them. The sesamoid bones, through their 

 ligamentous attachments, have a similar and more palpable de- 

 scending and ascending movement; a movement, indeed, that is 

 perfectly demonstrable in horses with long, oblique, bending pas- 

 terns. The navicular bone affords another example of the same 

 sort of mechanism. 



In considering the diseases of the first or more perfect class of 

 joints, the part we shall find it of most importance to make ourselves 

 well acquainted with, is the synovial or lining membrane. It is a 

 tissue similar in its composition to a serous membrane — to the peri- 

 toneum, the pleura, and the pericardium : like them, it is thin and 

 very vascular, and is furnished with the means of secretion. The 

 joint-oil or synovia, however, is a very different secretion from 

 that poured out by the serous tissue : this, as its name implies, is 

 serous or aqueous in its nature ; whereas the synovia has a good 

 deal of albumen in its composition — is, in fact, very like white of 

 egg. The synovial membrane being in itself, as was before ob- 

 served, a complete sac, having no opening into it, any wound admit- 

 ting air into the cavity of the joint and giving escape to the synovia, 

 we find, as might be anticipated, to be attended with serious con- 

 sequences : inflammation, intense in its character and destructive 

 in its tendency, is ever ready to follow such exposure, and that 

 treatment proves the best which most speedily seals up again the 

 cavity of the joint. But, seeing the synovial membrane^ — 'which 

 gives a complete lining to the interior of the joint, leaving no part 

 therein uncovered by it — is not the same kind of tissue in every 

 part (being, v/here it is reflected over the cartilaginous ends of the 

 bones, so extremely thin and pellucid that for many years its exist- 

 ence upon the cartilage was matter of dispute) inflammation in it, 

 as might be expected, is not attended with the same effects in one 

 part as in another. Augmented secretion, suppuration, thickening, 

 effusion of lymph, ulceration, may, one or other, or all in succession, 



